1. Field of the Invention
The present invention relates to an image forming apparatus with electron emitting elements.
2. Related Background Art
Attention has been paid to a thin flat type display because it requires less space and is light in weight so that it is expected that a CRT type display is replaced by the flat type display. Present flat type displays include a liquid crystal type, a plasma light emission type, and a multi electron source type. Of these, the plasma light emission type display and multi electron source type displays have a large angle of view and an image quality comparable to a CRT display, and can display an image of high definition.
Such an image forming apparatus has a rear plate, a face plate, a support frame, and spacers. The rear plate has an electron source made of a number of electron emitting elements. The face plate has a fluorescent member. The rear plate and face plate together with the support frame constitute a vacuum envelope. The spacers define the distance between the face and rear plates. As the electron emitting elements, cold cathode elements capable of being mounted at a high density have been developed, such as field emission type electron emitting elements which emit electrons from a conical or needle-like tip and surface conduction type electron emitting elements.
As a display area of a display becomes large, it becomes necessary to make the back and face plates thick in order to prevent the vacuum envelope from being deformed by a difference between the inner vacuum and external atmospheric pressure. This not only increases the weight of the display but also makes an image distorted as viewed obliquely. In order to make the vacuum envelope resistant against the atmospheric pressure by using relatively thin members, structure support members called spacers or ribs are disposed between the back and face plates. A distance between the back plate with the electron source and the face plate with the fluorescent member is maintained at sub-millimeter or several millimeter and the inside of the vacuum envelope is maintained at a high vacuum. In order to accelerate electrons emitted from the electron source, a high voltage of several hundred V or higher is applied between the fluorescent member and the electron source. Namely, a high electric field of an electric field intensity over 1 kV/mm is applied between the fluorescent member and the electron source. Electric discharge at the structure support member such as spacers is therefore feared.
A spacer is electrically charged when electrons emitted from the electron source or some electrons reflected from the fluorescent member side collide with the spacer or when positive ions ionized by emitted electrons attach the spacer. If the spacer is electrically charged, the trajectory of electrons emitted from the electron source may be bent and the electrons reach the fluorescent member at a position different from a normal position. Therefore, an image near at the spacer is displayed distorted as viewed from the face plate side.
In order to solve this problem, it has been proposed to flow a small current through the spacer to remove electric charges (e.g., JP-A-57-118355, JP-A-61-124031). According to this technique, a semiconductive film is formed on the surface of an insulating spacer to allow a small current to flow through the spacer surface. A charge preventive film used according to this technique is a tin oxide thin film, a thin film of mixed crystal of tin oxide and indium oxide, or a metal film.
A semiconductive thin film such as tin oxide used by the above-described technique is so sensitive to gas such as oxygen as to be applied to a gas sensor, so that the resistance value of the thin film is likely to be changed with ambient atmosphere. These materials and metal films have a small specific resistance. it is therefore necessary to form an island-shaped film or a very thin film in order to make it semiconductive. A conventional charge preventive film is therefore difficult to be formed and is likely to change its resistance value during a heat treatment such as frit sealing and baking during display manufacture steps.
It is an object of the invention to provide an image forming apparatus capable of forming a high quality image.
It is another object of the present invention to provide an image forming apparatus capable of forming a high quality image, by suppressing the influence of spacers disposed in the image forming apparatus upon the image forming performance as much as possible.
In order to achieve the above objects, the invention provides an image forming apparatus comprising: an envelope including as constituent elements first and second substrates spaced by some distance; an electron source and an image forming member for forming an image upon application of electrons from the electron source, the electron source and the image forming member being disposed in the envelope; and spacers for maintaining the distance between the first and second substrates, wherein the spacer is conductive and has a heat resistant organic polymer film formed on the surface of the spacer.
The invention also provides an image forming apparatus comprising: an envelope including as constituent elements first and second substrates spaced be some distance; an electron source and an image forming member for forming an image upon application of electrons from the electron source, the electron source and the image forming member being disposed in the envelope; and spacers for maintaining the distance between the first and second substrates, wherein the spacer comprises an insulating base member, a conductive film formed on the insulating base member, and a heat resistant organic polymer film formed on the conductive film.